Quantum interference device, atomic oscillator, electronic apparatus, and moving object

ABSTRACT

An atomic oscillator includes a gas cell into which alkali metal atoms are sealed, a light emitting portion that emits excitation light including a pair of resonance light beams for resonating the alkali metal atoms toward the alkali metal atoms, a coil that is provided to surround an outer circumference of the gas cell with an axis of the excitation light as an axial direction, and a shield case that stores at least the gas cell and the coil and contains a metal material, in which the shield case is constituted by a plurality of tabular portions, and, among the plurality of tabular portions, a main surface of one of two adjacent tabular portions faces a side surface of the other tabular portion.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/573,467 filed Dec. 17, 2014, which claims priority to Japanese PatentApplication No. 2013-263484 filed Dec. 20, 2013, both of which arehereby expressly incorporated by reference herein in their entireties.

BACKGROUND

1. Technical Field

The present invention relates to a quantum interference device, anatomic oscillator, an electronic apparatus, and a moving object.

2. Related Art

As for an oscillator which has a high accuracy oscillationcharacteristic for a long period of time, an atomic oscillator is knownwhich oscillates on the basis of energy transition of atoms of an alkalimetal such as rubidium or cesium (for example, refer toJP-A-2009-164331).

Generally, operation principles of the atomic oscillator are largelyclassified into a method of using a double resonance phenomenon causedby light and microwaves, and a method of using a quantum interferenceeffect (also referred to as coherent population trapping (CPT)) causedby two types of light beams with different wavelengths. Anatomicoscillator using the quantum interference effect can be madesmaller-sized than an atomic oscillator using the double resonancephenomenon, and thus has been recently expected to be mounted in variousapparatuses.

The atomic oscillator using the quantum interference effect, asdisclosed in JP-A-2009-164331, includes a gas cell into which gaseousmetal atoms are sealed; a semiconductor laser which irradiates the metalatoms in the gas cell with laser light including two types of resonancelight beams having different frequencies; and a light detector whichdetects the laser light which has been transmitted through the gas cell.In such an atomic oscillator, when a frequency difference between thetwo types of resonance light beams matches a specific value, neither ofthe two types of resonance light beams is absorbed by the metal atoms inthe gas cell and are transmitted. This is called an electromagneticallyinduced transparency (EIT) phenomenon, and an EIT signal which rapidlyincreases due to the EIT phenomenon is detected by the light detector.

Here, from the viewpoint of increasing detection accuracy of the lightdetector, the EIT signal preferably has a small line width (half width).Therefore, a coil which generates a magnetic field in a direction alongan optical axis of laser light is provided in the gas cell. By providingthe coil, gaps between degenerated other energy levels of the atoms ofthe alkali metal in the gas cell are enlarged by the Zeeman splitting,and thus resolution can be improved. Therefore, it is possible to reducea line width of the EIT signal.

In order to improve stability of a magnetic field in the gas cell, thegas cell and the coil are stored in a shield case (for example, refer toJP-A-2010-287937 and JP-A-2009-302118). JP-A-2010-287937 does notdisclose a specific method of forming the shield case. On the otherhand, JP-A-2009-302118 discloses that the shield case is formed byfolding a sheet metal. However, if the sheet metal is only folded, athickness of the shield case cannot be sufficiently secured at a partwhere edges of the sheet metal are close to or come into contact witheach other. For this reason, there is a problem in that a shield effectof the shield case decreases.

SUMMARY

An advantage of some aspects of the invention is to provide a quantuminterference device and an atomic oscillator, which stabilize a magneticfield in an inner space of a gas cell so as to reduce a line width of anEIT signal, thereby realizing good frequency stability, and also toprovide an electronic apparatus and a moving object, which include thequantum interference device and have high reliability.

The invention can be implemented as the following forms or applicationexamples.

Application Example 1

This application example is directed to a quantum interference deviceincluding: a gas cell into which metal atoms are sealed; a lightemitting portion that emits light including a pair of resonance lightbeams for resonating the metal atoms toward the metal atoms; a coil thatis provided to surround an outer circumference of the gas cell; and ashield case that stores the gas cell and the coil and contains a metalmaterial, in which the shield case is constituted by a plurality oftabular portions, and, among the plurality of tabular portions, a mainsurface of one of two adjacent tabular portions faces a side surface ofthe other tabular portion.

According to the quantum interference device according to thisapplication example, since the shield case is used, it is possible tostabilize a magnetic field in an inner space of the gas cell so as tofurther reduce a line width of an EIT signal, thereby realizing goodfrequency stability.

Application Example 2

In the quantum interference device according to the application example,it is preferable that the main surface intersects an axial direction ofthe coil.

With this configuration, it is possible to further stabilize a magneticfield in an inner space of the gas cell so as to further reduce a linewidth of an EIT signal, thereby realizing better frequency stability.

Application Example 3

In the quantum interference device according to the application example,it is preferable that the plurality of tabular portions include fivetabular portions.

With this configuration, it is possible to cover the gas cell and thecoil with the simple configuration.

Application Example 4

In the quantum interference device according to the application example,it is preferable that the shield case includes the plurality of tabularportions which are obtained by folding a single plate.

With this configuration, it is possible to simplify a configuration ofthe shield case and to contribute to miniaturization thereof.

Application Example 5

In the quantum interference device according to the application example,it is preferable that the main surface is joined to the side surface ata part where the main surface faces the side surface.

With this configuration, it is possible to reliably prevent an externalmagnetic field from entering the shield case and thus to furtherstabilize a magnetic field in the inner space of the gas cell.

Application Example 6

In the quantum interference device according to the application example,it is preferable that the metal material includes a soft magneticmaterial.

With this configuration, it is possible to further improve a shieldeffect by the shield case.

Application Example 7

In the quantum interference device according to the application example,it is preferable that the soft magnetic material is permalloy.

With this configuration, it is possible to considerably improve a shieldeffect by the shield case.

Application Example 8

This application example is directed to an atomic oscillator includingthe quantum interference device according to the application example.

With this configuration, it is possible to provide an atomic oscillatorwhich stabilizes a magnetic field in an inner space of the gas cell soas to reduce a line width of an EIT signal, thereby realizing goodfrequency stability.

Application Example 9

This application example is directed to an electronic apparatusincluding the quantum interference device according to the applicationexample.

With this configuration, it is possible to provide an electronicapparatus with high reliability.

Application Example 10

This application example is directed to a moving object including thequantum interference device according to the application example.

With this configuration, it is possible to provide a moving object withhigh reliability.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described with reference to the accompanyingdrawings, wherein like numbers reference like elements.

FIG. 1 is a schematic diagram illustrating a configuration of an atomicoscillator according to an embodiment of the invention.

FIG. 2 is a diagram illustrating an energy state of an alkali metal.

FIG. 3 is a graph illustrating a relationship between a frequencydifference between two light beams emitted from a light emittingportion, and an intensity of light detected by a light detectionportion.

FIG. 4 is an exploded perspective view of the atomic oscillatorillustrated in FIG. 1.

FIG. 5 is a longitudinal cross-sectional view of the atomic oscillatorillustrated in FIG. 1.

FIG. 6 is a schematic diagram illustrating a light emission portion anda gas cell included in the atomic oscillator illustrated in FIG. 1.

FIG. 7 is a perspective view (partially ruptured view) illustrating aschematic configuration of a gas cell assembly according to a firstembodiment.

FIG. 8 is a cross-sectional view taken along the line X-X in FIG. 7.

FIG. 9 is a development view of a shield case illustrated in FIG. 7.

FIG. 10 is a cross-sectional view, corresponding to FIG. 8, of a gascell assembly according to a second embodiment.

FIG. 11 is a cross-sectional view, corresponding to FIG. 8, of a gascell assembly according to a third embodiment.

FIG. 12 is a cross-sectional view, corresponding to FIG. 8, of a gascell assembly according to a fourth embodiment.

FIG. 13 is a perspective view (partially ruptured view) illustrating aschematic configuration of a gas cell assembly according to a fifthembodiment.

FIG. 14 is a development view of a shield case illustrated in FIG. 13.

FIG. 15 is a diagram illustrating a schematic system configuration in acase where the atomic oscillator according to the embodiments of theinvention is applied to a positioning system using a GPS satellite.

FIG. 16 is a diagram illustrating an example of a moving objectaccording to an embodiment of the invention.

FIG. 17 is a cross-sectional view, corresponding to FIG. 8, of a gascell assembly in which a shield case of the related art is used.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

Hereinafter, with reference to the accompanying drawings, a detaileddescription will be made of a quantum interference device, an atomicoscillator, an electronic apparatus, and a moving object according toembodiments of the invention.

1. Atom Oscillator (Quantum Interference Device)

First, an atomic oscillator (an atomic oscillator including a quantuminterference device according to an embodiment of the invention)according to an embodiment of the invention will be described. Inaddition, hereinafter, an example in which a quantum interference deviceaccording to an embodiment of the invention is applied to an atomicoscillator will be described, but the invention is not limited thereto,and the quantum interference device is applicable to, for example, amagnetic sensor and a quantum memory.

FIG. 1 is a schematic diagram illustrating an atomic oscillatoraccording to an embodiment of the invention. In addition, FIG. 2 is adiagram illustrating an energy state of an alkali metal, and FIG. 3 is agraph illustrating a relationship between a frequency difference betweentwo light beams emitted from a light emitting portion, and an intensityof light detected by a light detection portion.

The atomic oscillator (quantum interference device) 1 illustrated inFIG. 1 uses a quantum interference effect.

The atomic oscillator 1, as illustrated in FIG. 1, includes a first unit2 which is a unit of a light emission side, a second unit 3 which is aunit of a light detection side, optical components 41, 42 and 43provided between the units 2 and 3, and a controller 6 which controlsthe first unit 2 and the second unit 3.

Here, the first unit 2 includes a light emitting portion 21 and a firstpackage 22 which stores the light emitting portion 21.

The second unit 3 includes a gas cell 31, a light detection portion 32,a heater 33, a temperature sensor 34, a coil 35, and a second package 36which stores the above-described elements. The gas cell 31 and the coil35 are stored in a shield case 9.

First, a principle of the atomic oscillator 1 will be described briefly.

As illustrated in FIG. 1, in the atomic oscillator 1, the light emittingportion 21 emits excitation light LL toward the gas cell 31, and thelight detection portion 32 detects the excitation light LL which hasbeen transmitted through the gas cell 31.

A gaseous alkali metal (metal atoms) is sealed into the gas cell 31. Thealkali metal has energy levels of a three-level system as illustrated inFIG. 2, and may take three states including two ground states (groundstates 1 and 2) with different energy levels and an excited state. Here,the ground state 1 is an energy state lower than the ground state 2.

The excitation light LL emitted from the light emitting portion 21includes two types of resonance light beams 1 and 2 which have differentfrequency. When the above-described gaseous alkali metal is irradiatedwith the two types of resonance light beams 1 and 2, light absorptance(light transmittance) of the resonance light beams 1 and 2 in the alkalimetal varies depending on a difference (ω₁-ω₂) between a frequency ω₁ ofthe resonance light 1 and a frequency ω₂ of the resonance light 2.

When the difference (ω₁-ω₂) between the frequency ω₁ of the resonancelight 1 and the frequency ω₂ of the resonance light 2 matches afrequency corresponding to an energy difference between the ground state1 and the ground state 2, excitation from the ground states 1 and 2 tothe excited state stops, respectively. At this time, neither of theresonance light beams 1 and 2 is absorbed by the alkali metal, but bothare transmitted therethrough. This phenomenon is called a CPT phenomenonor an electromagnetically induced transparency (EIT) phenomenon.

For example, if the light emitting portion 21 fixes the frequency ω₁ ofthe resonance light 1 to a certain value and changes the frequency ω₂ ofthe resonance light 2, when the difference (ω₁-ω₂) between the frequencyω₁ of the resonance light 1 and the frequency ω₂ of the resonance light2 matches a frequency ω₀ corresponding to an energy difference betweenthe ground state 1 and the ground state 2, an intensity detected by thelight detection portion 32 rapidly increases as illustrated in FIG. 3.This rapidly increasing signal is detected as an EIT signal. The EITsignal has an inherent value which is defined by the kind of alkalimetal. Therefore, an oscillator can be formed by using such an EITsignal.

Hereinafter, a specific configuration of the atomic oscillator 1according to the present embodiment will be described.

FIG. 4 is an exploded perspective view of the atomic oscillatorillustrated in FIG. 1, and FIG. 5 is a longitudinal cross-sectional viewof the atomic oscillator illustrated in FIG. 1.

In addition, in FIGS. 4 and 5 (the same for FIGS. 7 and 8, and FIGS. 10to 13, and FIG. 17), for convenience of description, an X axis, a Yaxis, a Z axis are illustrated as three axes which are perpendicular toeach other, and a tip end side of each arrow illustrated in each drawingis referred to as “+(positive) side”, and a base end side is referred toas “−(negative) side”. Further, hereinafter, for convenience ofdescription, a direction parallel to the X axis is referred to as an “Xaxis direction”, a direction parallel to the Y axis is referred to as a“Y axis direction”, and a direction parallel to the Z axis is referredto as a “Z axis direction”. In addition, a +Z direction side (a top sidein each drawing) is referred to as an “upper side”, and a −Z directionside (a bottom side in each drawing) is referred to as a “lower side”.

The atomic oscillator 1, as illustrated in FIG. 4, includes a wiringboard 5 (support member) in which the controller 6 is mounted and whichholds the first unit 2, the second unit 3, and the optical components41, 42 and 43, and connectors 71 and 72 which electrically connect thefirst unit 2 and the second unit 3 to the wiring board 5.

The first unit 2 and the second unit 3 are electrically connected to thecontroller 6 via a wiring (not illustrated) of the wiring board 5 andthe connectors 71 and 72 and are controlled to be driven by thecontroller 6.

Hereinafter, each part of the atomic oscillator 1 will be described inorder.

First Unit

As described above, the first unit 2 includes the light emitting portion21 and the first package 22 which stores the light emitting portion 21.

Light Emitting Portion

The light emitting portion 21 has a function of emitting the excitationlight LL for exciting alkali metal atoms in the gas cell 31.

More specifically, the light emitting portion 21 emits light includingthe above-described two types of light beams (the resonance light 1 andthe resonance light 2) as the excitation light LL.

The frequency ω₁ of the resonance light 1 can excite (resonate) thealkali metal in the gas cell 31 from the above-described ground state 1to the excited state.

The frequency ω₂ of the resonance light 2 can excite (resonate) thealkali metal in the gas cell 31 from the above-described ground state 2to the excited state.

The light emitting portion 21 is not particularly limited as long as theabove-described excitation light LL can be emitted, but, for example, asemiconductor laser such as a vertical cavity surface emitting laser(VCSEL) may be used.

In addition, a temperature of the light emitting portion 21 is adjustedto a predetermined temperature by a temperature adjustment element (aheating resistor, a Peltier element, or the like) (not illustrated).

First Package

The first package 22 stores the above-described light emitting portion21.

As illustrated in FIG. 5, the first package 22 includes a base 221(first base) and a lid 222 (first lid).

The base 221 directly or indirectly supports the light emitting portion21. In the present embodiment, the base 221 is tabular, and is circularin a plan view.

The light emitting portion 21 (mounted component) is installed (mounted)on one surface (mounted surface) of the base 221. As illustrated in FIG.5, a plurality of leads 223 protrude from the other surface of the base221. The plurality of leads 223 are electrically connected to the lightemitting portion 21 via a wiring (not illustrated).

The base 221 is joined to the lid 222 which covers the light emittingportion 21 on the base 221.

The lid 222 has a bottomed tubular shape of which one end is open. Inthe present embodiment, the tubular portion of the lid 222 iscylindrical.

The opening of one end of the lid 222 is closed by the base 221.

A window portion 23 is provided at the other end of the lid 222, thatis, on a bottom opposite to the opening of the lid 222.

The window portion 23 is provided on an optical axis (an axis a of theexcitation light LL) between the gas cell 31 and the light emittingportion 21.

The window portion 23 transmits the excitation light LL therethrough.

In the present embodiment, the window portion 23 is a lens.Consequently, the excitation light LL can be applied to the gas cell 31without any waste.

The window portion 23 has a function of converting the excitation lightLL into parallel light. That is, the window portion 23 is a collimatorlens, and the excitation light LL in an inner space S is parallel light.Thus, it is possible to increase the number of alkali metal atoms whichare resonated by the excitation light LL emitted from the light emittingportion 21, among the alkali metal atoms present in the inner space S.As a result, it is possible to increase an intensity of the EIT signal.

The window portion 23 is not limited to the lens as long as theexcitation light LL can be transmitted therethrough, and may be, forexample, optical components other than a lens, and may be a simplelight-transmissive tabular member. In this case, the lens having theabove-described function may be provided between the first package 22and the second package 36 in the same manner as the optical components41, 42 and 43 described later.

Materials forming the portions of the lid 222 other than the windowportion 23 are not particularly limited, but, for example, ceramics, ametal, or a resin may be used.

Here, in a case where the portions of the lid 222 other than the windowportion 23 are made of a material which transmits the excitation lighttherethrough, the portions of the lid 222 other than the window portion23 may be integrally formed with the window portion 23. In addition, ina case where the portions of the lid 222 other than the window portion23 are made of a material which does not transmit the excitation lighttherethrough, the portions of the lid 222 other than the window portion23 may be formed separately from the window portion 23, and may bejoined thereto by using well-known joint methods.

The base 221 and the lid 222 are preferably air-tightly joined to eachother. In other words, a space in the first package 22 is preferablyair-tightly formed. Consequently, the first package 22 can be made in adecompressed state or in an inert gas sealed state, and, as a result, itis possible to improve characteristics of the atomic oscillator 1.

A joint method of the base 221 and the lid 222 is not particularlylimited, but, for example, brazing, seam welding, or energy ray welding(laser welding, electron ray welding, or the like) may be used.

A joint member for joining the base 221 to the lid 222 may be interposedtherebetween.

Components other than the light emitting portion 21 may be stored in thefirst package 22.

For example, a temperature adjustment element which adjusts atemperature of the light emitting portion 21 or a temperature sensor maybe stored in the first package 22. As such a temperature adjustmentelement, for example, there may be a heating resistor (heater) or aPeltier element.

According to the first package 22 configured to include the base 221 andthe lid 222, the first package 22 can store the light emitting portion21 while allowing the excitation light from the light emitting portion21 to be emitted to the outside of the first package 22.

The first package 22 is held at the wiring board 5, described later, sothat the base 221 is disposed on an opposite side to the second package36.

Second Unit

As described above, the second unit 3 includes the gas cell 31, thelight detection portion 32, the heater 33, the temperature sensor 34,the coil 35, and the second package 36 which stores the above-describedelements. In addition, as described above, the gas cell 31 and the coil35 are stored in the shield case 9.

Gas Cell

An alkali metal such as gaseous rubidium, cesium or sodium is sealedinto the gas cell 31. A rare gas such as argon or neon, or an inert gassuch as nitrogen may be sealed as a buffer gas in the gas cell 31 alongwith the alkali metal gas as necessary.

For example, as illustrated in FIG. 6, the gas cell 31 includes a mainbody 311 which has a columnar through hole 311 a, and a pair of windows312 and 313 which seal both openings of the through hole 311 a. Thus,the inner space S in which the above-described alkali metal is sealed isformed.

A material forming the main body 311 is not particularly limited, but,for example, a metal material, a resin material, a glass material, asilicon material, quartz crystal, or the like may be used. From theviewpoint of workability or joining with the windows 312 and 313, theglass material or the silicon material is preferably used.

The main body 311 is air-tightly joined to the windows 312 and 313.Consequently, the inner space S of the gas cell 31 can be formed as anair-tight space.

A method of joining the main body 311 to the windows 312 and 313 is notparticularly limited as long as the method is defined according to aforming material, but, for example, a joint method using an adhesive, adirect joint method, and an anodic joint method may be used.

A material forming the windows 312 and 313 is not particularly limitedas long as the material can transmit the excitation light LLtherethrough, but, for example, a silicon material, a glass material, orquartz crystal may be used.

The windows 312 and 313 transmit the excitation light LL from the lightemitting portion 21 therethrough. One window 312 transmits theexcitation light LL which is incident to the gas cell 31 therethrough,and the other window 313 transmits the excitation light LL which isemitted out of the gas cell 31 therethrough.

The gas cell 31 is heated by the heater 33 so as to be adjusted to apredetermined temperature.

Light Detection Portion

The light detection portion 32 has a function of detecting an intensityof the excitation light LL (the resonance light beams 1 and 2) which hasbeen transmitted through the gas cell 31.

The light detection portion 32 is not particularly limited as long asthe excitation light can be detected, but, for example, a light detector(light receiving element) such as a solar cell or a photodiode may beused.

Heater

The heater 33 has a function of heating the above-described gas cell 31(more specifically, the alkali metal in the gas cell 31). Thus, thealkali metal in the gas cell 31 can be maintained in a gaseous phase ofa desired concentration.

The heater 33 generates heat due to conduction, and is formed by, forexample, a heating resistor provided on an outer surface of the gas cell31. This heating resistor is formed by using, for example, a chemicalvapor deposition method (CVD) such as plasma CVD or thermal CVD, a dryplating method such as vacuum deposition, or a sol/gel method.

Here, in a case where the heating resistor is provided at an incidenceportion or an emission portion of the excitation light LL in the gascell 31, the heating resistor is made of a material which transmits theexcitation light therethrough, specifically, a transparent electrodematerial such as an oxide, for example, indium tin oxide (ITO), indiumzinc oxide (IZO), In₃O₃, SnO₂, Sb-containing SnO₂, or Al-containing ZnO.

The heater 33 is not particularly limited as long as the gas cell 31 canbe heated, and may not be in contact with the gas cell 31. In addition,the gas cell 31 may be heated by using a Peltier element instead of theheater 33 or along with the heater 33.

The heater 33 is electrically connected to a temperature control portion62 of the controller 6, described later, so as to be conducted.

Temperature Sensor

The temperature sensor 34 detects a temperature of the heater 33 or thegas cell 31. In addition, a heating amount of the above-described heater33 is controlled on the basis of a detection result from the temperaturesensor 34. Thus, the alkali metal atoms in the gas cell 31 can bemaintained at a desired temperature.

In addition, a position where the temperature sensor 34 is installed isnot particularly limited, and, for example, the temperature sensor 34may be installed on the heater 33, and may be installed on the outersurface of the gas cell 31.

The temperature sensor 34 is not particularly limited, and well-knowntemperature sensors such as a thermistor and a thermocouple may be used.

The temperature sensor 34 is electrically connected to the temperaturecontrol unit 62 of the controller 6, described later, via a wiring (notillustrated).

Coil

The coil 35 has a function of generating a magnetic field in thedirection (parallel direction) along the axis a of the excitation lightLL in the inner space S. Thus, gaps between degenerated other energylevels of the alkali metal atoms in the inner space S are enlarged bythe Zeeman splitting, and thus resolution can be improved. As a result,it is possible to reduce a line width of the EIT signal.

A magnetic field generated by the coil 35 may be either a DC magneticfield or an AC magnetic field, and a magnetic field is obtained when aDC magnetic field overlaps an AC magnetic field.

An installation position of the coil 35 is not particularly limited. Forexample, a pair of coils may oppose each other with the gas cell 31interposed therebetween so as to form Helmholtz coils, but, in thepresent embodiment, the coil 35 is wound along an outer circumference ofthe gas cell 31 so as to form a solenoid coil. This configuration willbe described later in detail.

The coil 35 is electrically connected to a magnetic field controlportion 63 of the controller 6, described later, via a wiring (notillustrated). Thus, the coil 35 can be conducted.

Second Package

The second package 36 stores the gas cell 31, the light detectionportion 32, the heater 33, the temperature sensor 34, and the coil 35.

The second package 36 is formed in the same manner as the first package22 of the first unit 2.

Specifically, as illustrated in FIG. 5, the second package 36 includes abase 361 (second base) and a lid 362 (second lid).

The base 361 directly or indirectly supports the gas cell 31, the lightdetection portion 32, the heater 33, the temperature sensor 34, and thecoil 35. In the present embodiment, the base 361 is tabular, and iscircular in a plan view.

The gas cell 31, the light detection portion 32, the heater 33, thetemperature sensor 34, and the coil 35 (a plurality of mountedcomponents) are installed (mounted) on one surface of the base 361. Asillustrated in FIG. 5, a plurality of leads 363 protrude from the othersurface of the base 361. The plurality of leads 363 are electricallyconnected to the light detection portion 32, the heater 33, thetemperature sensor 34, and the coil 35 via wirings (not illustrated).

The base 361 is joined to a lid 362 which covers the gas cell 31, thelight detection portion 32, the heater 33, the temperature sensor 34,and the coil 35 on the base 361.

The lid 362 has a bottomed tubular shape of which one end is open. Inthe present embodiment, the tubular portion of the lid 362 iscylindrical.

The opening of one end of the lid 362 is closed by the base 361.

A window portion 37 is provided at the other end of the lid 362, thatis, on a bottom opposite to the opening of the lid 362.

The window portion 37 is provided on the optical axis (the axis a)between the gas cell 31 and the light emitting portion 21.

The window portion 37 transmits the above-described excitation lighttherethrough.

In the present embodiment, the window portion 37 is made of alight-transmissive tabular member.

The window portion 37 is not limited to the light-transmissive tabularmember as long as the excitation light can be transmitted therethrough,and may be, for example, an optical component such as a lens, apolarization plate, or a λ/4 wavelength plate.

Materials forming the portions of the lid 362 other than the windowportion 37 are not particularly limited, but, for example, ceramics, ametal, or a resin may be used.

Here, in a case where the portions of the lid 362 other than the windowportion 37 are made of a material which transmits the excitation lighttherethrough, the portions of the lid 362 other than the window portion37 may be integrally formed with the window portion 37. In addition, ina case where the portions of the lid 362 other than the window portion37 are made of a material which does not transmit the excitation lighttherethrough, the portions of the lid 362 other than the window portion37 may be formed separately from the window portion 37, and may bejoined thereto by using well-known joint methods.

The base 361 and the lid 362 are preferably air-tightly joined to eachother. In other words, a space in the second package 36 is preferablyair-tightly formed. Consequently, the second package 36 can be made in adecompressed state or in an inert gas sealed state, and, as a result, itis possible to improve characteristics of the atomic oscillator 1.

A joint method of the base 361 and the lid 362 is not particularlylimited, but, for example, brazing, seam welding, or energy ray welding(laser welding, electron ray welding, or the like) may be used.

A joint member for joining the base 361 to the lid 362 may be interposedtherebetween.

At least the gas cell 31, the light detection portion 32, and the coil35 may be stored in the second package 36, and components other than thegas cell 31, the light detection portion 32, the heater 33, thetemperature sensor 34, and the coil 35 may be stored therein.

According to the second package 36 configured to include the base 361and the lid 362, the second package 36 can store the gas cell 31, thelight detection portion 32, and the coil 35 while allowing theexcitation light from the light emitting portion 21 to be incident tothe second package 36. Therefore, the second package 36 is used incombination with the first package 22, and thus it is possible to storethe light emitting portion 21 and the gas cell 31 in the differentpackages which are not in contact with each other while securing theoptical path of the excitation light from the light emitting portion 21to the light detection portion 32 via the gas cell 31.

The second package 36 is held at the wiring board 5, described later, sothat the base 361 is disposed on an opposite side to the first package22.

Optical Components

The plurality of optical components 41, 42 and 43 are provided betweenthe first package 22 and the second package 36. The plurality of opticalcomponents 41, 42 and 43 are provided on the optical axis (the axis a)between the light emitting portion 21 in the first package 22 and thegas cell 31 in the second package 36.

Here, in the present embodiment, the optical component 41, the opticalcomponent 42, and the optical component 43 are disposed in this orderfrom the first package 22 side to the second package 36 side.

The optical component 41 is a λ/4 wavelength plate. Thus, for example,in a case where excitation light from the light emitting portion 21 islinearly polarized light, the excitation light can be converted intocircularly polarized light (right-handed circularly polarized light orleft-handed circularly polarized light).

As described above, in a state in which the alkali metal atoms in thegas cell 31 are Zeeman-split by a magnetic field of the coil 35, iflinearly polarized excitation light is applied to the alkali metalatoms, the alkali metal atoms are uniformly distributed to and arepresent in a plurality of levels in which the alkali metal atoms areZeeman-split due to an interaction between the excitation light and thealkali metal atoms. As a result, since the number of alkali metal atomswith a desired energy level becomes relatively smaller than the numberof alkali metal atoms with other energy levels, the number of atomsshowing a desired EIT phenomenon is reduced, thus an intensity of adesired EIT signal decreases, and, as a result, an oscillationcharacteristic of the atomic oscillator 1 deteriorates.

In contrast, as described above, in a state in which the alkali metalatoms in the gas cell 31 are Zeeman-split by a magnetic field of thecoil 35, if circularly polarized excitation light is applied to thealkali metal atoms, due to an interaction between the excitation lightand the alkali metal atoms the number of alkali metal atoms with adesired energy level can be made relatively larger than the number ofalkali metal atoms with other energy levels among a plurality of levelsin which the alkali metal atoms are Zeeman-split. For this reason, thenumber of atoms showing a desired EIT phenomenon increases, thus anintensity of a desired EIT signal also increases, and, as a result, anoscillation characteristic of the atomic oscillator 1 can be improved.

In the present embodiment, the optical component 41 has a disc shape.For this reason, the optical component 41 can be rotated about an axialline which is parallel to the optical axis (the axis a) in a state ofbeing engaged with a through hole 53 having a shape, described later. Ashape of the optical component 41 in a plan view is not limited thereto,and may be a polygonal shape such as a quadrangular or pentagonal shape.

The optical components 42 and 43 are disposed on the second unit 3 sideso as to correspond to the optical component 41.

The optical components 42 and 43 are dimming filters (ND filters). Thus,an intensity of the excitation light LL which is incident to the gascell 31 can be adjusted (reduced). For this reason, even in a case wherean output level of the light emitting portion 21 is high, the excitationlight incident to the gas cell 31 can be adjusted to a desired lightamount. In the present embodiment, an intensity of the excitation lightLL which has been converted into circularly polarized light by theoptical component 41 is adjusted by the optical components 42 and 43.

In the present embodiment, each of the optical components 42 and 43 istabular. A shape of each of the optical components 42 and 43 in a planview is circular. For this reason, each of the optical components 42 and43 can be rotated about an axial line which is parallel to the opticalaxis (the axis a) in a state of being engaged with the through hole 53having a shape, described later.

A shape of each of the optical components 42 and 43 in a plan view isnot limited thereto, and may be a polygonal shape such as a quadrangularor pentagonal shape.

Dimming rates of the optical component 42 and the optical component 43may or may not be the same as each other.

The optical components 42 and 43 may have portions of which dimmingrates are different continuously or stepwise on the upper sides and thelower sides. In this case, positions of the optical components 42 and 43are adjusted vertically with respect to the wiring board 5, and thus adimming rate of the excitation light can be adjusted.

Each of the optical components 42 and 43 may have a portion of which adimming rate is different continuously or intermittently in acircumferential direction. In this case, the optical components 42 and43 are rotated, and thus a dimming rate of the excitation light can beadjusted. In addition, in this case, a rotation center of the opticalcomponents 42 and 43 may be deviated from the axis a.

One of the optical components 42 and 43 may be omitted. In a case wherean output level of the light emitting portion 21 is appropriate, both ofthe optical components 42 and 43 may be omitted.

The optical components 41, 42 and 43 are not limited to the types, thearrangement order, the number thereof described above, and the like. Forexample, the optical components 41, 42 and 43 are not limited to the λ/4wavelength plate or the dimming filter, respectively, and may be lenses,polarization plates, or the like.

Wiring Board

The wiring board 5 has wires (not illustrated), and has a function ofelectrically connecting electronic components such as the controller 6mounted on the wiring board 5 to the connectors 71 and 72 via the wires.

The wiring board 5 has a function of holding the first package 22, thesecond package 36, and the plurality of optical components 41, 42 and43.

The wiring board 5 holds the first package 22 and the second package 36which are not in contact with each other with a space interposedtherebetween. Consequently, thermal interference between the lightemitting portion 21 and the gas cell 31 is prevented or minimized, andthus temperatures of the light emitting portion 21 and the gas cell 31can be controlled independently from each other.

Specifically, as illustrated in FIG. 4, the wiring board 5 is providedwith through holes 51, 52, 53, 54 and 55 which penetrate in a thicknessdirection thereof.

Here, the through hole 51 (first through hole) is provided on one endside of the wiring board 5 in the X axis direction, and the through hole52 (second through hole) is provided on the other end side of the wiringboard 5 in the X axis direction. The through holes 53, 54 and 55 (thirdthrough holes) are provided between the through hole 51 and the throughhole 52 of the wiring board 5.

In the present embodiment, the through holes 51, 52, 53, 54, 55 areformed independently from each other. For this reason, it is possible toincrease rigidity of the wiring board 5.

Part of the first package 22 is inserted into the through hole 51 fromthe upper side, and thus the first package 22 is positioned in the Xaxis direction, the Y axis direction, and the Z axis direction withrespect to the wiring board 5.

In the present embodiment, a width of the through hole 51 in the Y axisdirection is smaller than a width (a diameter of the cylindricalportion) of the first package 22 in the Y axis direction. For thisreason, the first package 22 is engaged (in contact) with an edge of thethrough hole 51 in a state in which the central axis of the cylindricalportion is located above the wiring board 5.

If the first package 22 is in contact with the edge of the through hole51, a contact area between the first package 22 and the wiring board 5can be reduced. Consequently, it is possible to minimize transmission ofheat between the first package 22 and the wiring board 5.

Similarly, part of the second package 36 is inserted into the throughhole 52 from the upper side, and thus the second package 36 ispositioned in the X axis direction, the Y axis direction, and the Z axisdirection with respect to the wiring board 5. In the same manner as inthe first package 22, the second package 36 is in contact with the edgeof the through hole 52, and thus a contact area between the secondpackage 36 and the wiring board 5 can be reduced. Consequently, it ispossible to minimize transmission of heat between the second package 36and the wiring board 5.

As mentioned above, it is possible to minimize heat transmission betweenthe first package 22 and the second package 36 through the wiring board5 and thus to minimize thermal interference between the light emittingportion 21 and the gas cell 31.

According to the wiring board 5 provided with such through holes 51 and52, the first package 22 and the second package 36 are installed at thewiring board 5, and thus an optical system including the light emittingportion 21 and the light detection portion 32 can be positioned. Forthis reason, the first package 22 and the second package 36 can beeasily installed at the wiring board 5.

When compared with a case where members holding the first package 22 andthe second package 36 are provided separately from the wiring pattern 5,it is possible to reduce the number of components. As a result, it ispossible to achieve low cost and miniaturization of the atomicoscillator 1.

In the present embodiment, as described above, since the through hole 51into which the first package 22 is inserted and the through hole 52 intowhich the second package 36 is inserted are formed separately from eachother at the wiring board 5, it is possible to increase the rigidity ofthe wiring board 5 and also to hold the first package 22 and the secondpackage 36 at the wiring board 5.

Part of the optical component 41 is inserted into the through hole 53,and thus the optical component 41 is positioned in the X axis direction,the Y axis direction, and the Z axis direction with respect to thewiring board 5.

Similarly, part of the optical component 42 is inserted into the throughhole 54, and thus the optical component 42 is positioned in the X axisdirection, the Y axis direction, and the Z axis direction with respectto the wiring board 5.

In addition, part of the optical component 43 is inserted into thethrough hole 55, and thus the optical component 43 is positioned in theX axis direction, the Y axis direction, and the Z axis direction withrespect to the wiring board 5.

According to the wiring board 5 having the through holes 53, 54 and 55,since the optical components 41, 42 and 43 are held thereat, the opticalcomponents 41, 42 and 43 can be installed in the wiring board whileadjusting positions or attitudes thereof, in a state in which the firstpackage 22 and the second package 36 are held at the wiring board 5,when each component is installed in the wiring board 5 duringmanufacturing of the atomic oscillator 1.

The through hole 53 can hold the optical component 41 to be rotatedabout an axial line (for example, the axis a) along a line segment whichconnects the first package 22 to the second package 36. Therefore, anattitude of the optical component 41 about the axis a can be adjusted ina state in which the optical component 41 is engaged with the throughhole 53 of the wiring board 5 and is thus positioned in a directionparallel to the axis a.

Similarly, the through hole 54 can hold the optical component 42 to berotated about an axial line along the line segment which connects thefirst package 22 to the second package 36. In addition, the through hole55 can hold the optical component 43 to be rotated about an axial linealong the line segment which connects the first package 22 to the secondpackage 36.

In the present embodiment, the through holes 53, 54 and 55 are formed sothat plate surfaces of the optical components 41, 42 and 43 are parallelto each other. In addition, the through holes 53, 54 and 55 are formedso that each of the plate surfaces of the optical components 41, 42 and43 is perpendicular to the axis a. The through holes 53, 54 and 55 maybe formed so that the plate surfaces of the optical components 41, 42and 43 are not parallel to each other, and may be formed so that each ofthe plate surfaces of the optical components 41, 42 and 43 is tiltedwith respect to the axis a.

Here, as described above, since the optical component 41 is a λ/4wavelength plate, an attitude of the optical component 41 is adjusted byrotating the optical component 41 regardless of an attitude of the firstpackage 22 relative to the wiring board 5, and thus the excitation lightfrom the light emitting portion 21 can be converted from linearlypolarized light into circularly polarized light.

When the optical components 41, 42 and 43 are installed in the wiringboard 5, first, for example, the first unit 2 and the second unit 3 areinstalled in and fixed to the wiring board 5. Then, at least one ofpositions and attitudes of the optical components 41, 42 and 43 arechanged while checking an EIT signal in a state in which the opticalcomponents 41, 42 and 43 are respectively engaged with the correspondingthrough holes 53, 54 and 55. When a desired EIT signal is confirmed, theoptical components 41, 42 and 43 are fixed to the wiring board 5 in thisstate. This fixation is not particularly limited, but may be performedby using, for example, a light curable adhesive. Even if the lightcurable adhesive is supplied to each of the through holes 53, 54 and 55before being cured, positions or attitudes of each of the opticalcomponents 41, 42 and 43 can be changed, and thus the light curableadhesive can be cured at a desired time in a short period of time inorder to fix the through holes to the wiring board 5.

Various print wiring boards may be used as the wiring board 5, but, asdescribed above, a board having a rigid portion, for example, a rigidboard or a flexible rigid board is preferably used from the viewpoint ofensuring the rigidity which is required to maintain a positionalrelationship between the held first package 22, second package 36, andoptical components 41, 42 and 43.

Even in a case where a wiring board (for example, a flexible board) nothaving a rigid portion is used as the wiring board 5, for example, areinforcing member for improving rigidity is joined to the wiring board,and thus it is possible to maintain a positional relationship betweenthe first package 22, the second package 36, and the optical components41, 42 and 43.

The controller 6 and the connectors 71 and 72 are installed on onesurface of the wiring board 5. Electronic components other than thecontroller 6 may be mounted on the wiring board 5.

Controller

The controller 6 illustrated in FIG. 1 has a function of controllingeach of the heater 33, the coil 35, and the light emitting portion 21.

In the present embodiment, the controller 6 is constituted by anintegrated circuit (IC) chip mounted on the wiring board 5.

The controller 6 includes the excitation light control portion 61 whichcontrols frequencies of the resonance light beams 1 and 2 from the lightemitting portion 21, the temperature control portion 62 which controls atemperature of the alkali metal in the gas cell 31, and the magneticfield control portion 63 which controls a magnetic field applied to thegas cell 31.

The excitation light control portion 61 controls frequencies of theresonance light beams 1 and 2 which are emitted from the light emittingportion 21 on the basis of a detection result from the above-describedlight detection portion 32. More specifically, the excitation lightcontrol portion 61 controls frequencies of the resonance light beams 1and 2 emitted from the light emitting portion 21 so that the frequencydifference (ω₁-ω₂) detected by the light detection portion 32 becomesthe inherent frequency ω₀ of the alkali metal.

In addition, although not illustrated, the excitation light controlportion 61 is provided with a voltage controlled quartz crystaloscillator (oscillation circuit), and outputs an oscillation frequencyof the voltage controlled quartz crystal oscillator as an output signalof the atomic oscillator 1 while synchronously adjusting the oscillationfrequency on the basis of a detection result from the light detectionportion 32.

In addition, the temperature control portion 62 controls a current whichflows to the heater 33 on the basis of a detection result from thetemperature sensor 34. Thus, the gas cell 31 can be maintained in adesired temperature range.

Further, the magnetic field control portion 63 controls a current whichflows to the coil 35 so as to make a magnetic field generated by thecoil 35 constant.

Connectors

The connector 71 (first connector) is installed at the first package 22and has a function of electrically connecting the light emitting portion21 to the wiring board 5. Consequently, the light emitting portion 21 inthe first package 22 is electrically connected to the controller 6 viathe connector 71.

The connector 72 (second connector) is installed at the second package36 and has a function of electrically connecting the light detectionportion 32 and the like to the wiring board 5. Consequently, the lightdetection portion 32, the heater 33, the temperature sensor 34, and thecoil 35 in the second package 36 are electrically connected to thecontroller 6 via the connector 72.

As illustrated in FIG. 4, the connector 71 includes a connector portion712 which is installed at the first package 22, a fixation portion 713which is fixed to the wiring board 5, and a cable portion 714 whichconnects the connector portion 712 to the fixation portion 713.

The connector portion 712 has a sheet shape, and has a plurality ofthrough holes 711 which penetrate in a thickness direction thereof.

The plurality of through holes 711 are provided so as to correspond tothe plurality of leads 223 of the first package 22. The plurality ofleads 223 are respectively inserted into the plurality of through holes711 so as to correspond thereto.

The plurality of leads 223 are fixed to the connector portion 712 asillustrated in FIG. 5, for example, via solder, and are electricallyconnected to wires (not illustrated) provided at the connector portion712.

On the other hand, the fixation portion 713 has a sheet shape and isfixed to the wiring board 5 as illustrated in FIG. 5, for example, viaan anisotropic conductive adhesive (ACF). Wires (not illustrated)provided at the fixation portion 713 are electrically connected to wires(not illustrated) of the wiring board 5.

The wires (not illustrated) of the fixation portion 713 are electricallyconnected to the wires (not illustrated) of the connector portion 712via wires (not illustrated) provided at the cable portion 714.

In the same manner as the above-described connector 71, as illustratedin FIG. 4, the connector 72 includes a connector portion 722 which isinstalled at the second package 36, a fixation portion 723 which isfixed to the wiring board 5, and a cable portion 724 which connects theconnector portion 722 to the fixation portion 723.

The connector portion 722 has a sheet shape, and has a plurality ofthrough holes 721 which penetrate in a thickness direction thereof.

The plurality of through holes 721 are provided so as to correspond tothe plurality of leads 363 of the second package 36. The plurality ofleads 363 are respectively inserted into the plurality of through holes721 so as to correspond thereto.

The plurality of leads 363 are fixed to the connector portion 722 asillustrated in FIG. 5, for example, via solder, and are electricallyconnected to wires (not illustrated) provided at the connector portion722.

On the other hand, the fixation portion 723 has a sheet shape and isfixed to the wiring board 5 as illustrated in FIG. 5, for example, viaan anisotropic conductive adhesive (ACF). Wires (not illustrated)provided at the fixation portion 723 are electrically connected to wires(not illustrated) of the wiring board 5.

The wires (not illustrated) of the fixation portion 723 are electricallyconnected to the wires (not illustrated) of the connector portion 722via wires (not illustrated) provided at the cable portion 724.

The connectors 71 and 72 are respectively constituted by flexibleboards. In other words, in the connector 71, the connector portion 712,the fixation portion 713, and the cable portion 714 are respectivelyflexible boards, and the connector portion 712, the fixation portion713, and the cable portion 714 are integrally formed together.Similarly, in the connector 72, the connector portion 722, the fixationportion 723, and the cable portion 724 are respectively flexible boards,and the connector portion 722, the fixation portion 723, and the cableportion 724 are integrally formed together.

The connectors 71 and 72 constituted by the flexible boards are used,and thus it is possible to achieve low cost and miniaturization of theatomic oscillator 1.

The electrical connection between the light emitting portion 21 and thewiring board 5 and the electrical connection between the light detectionportion 32 and the like and the wiring board 5 are not limited to theabove-described connectors 71 and 72, and may be performed, for example,by using the connector portions having a socket shape.

In the above-described atomic oscillator 1, a gas cell assembly in whichthe gas cell 31 and the coil 35 are stored in the shield case 9 isprovided (mounted) in the second package 36. Hereinafter, aconfiguration of the gas cell assembly will be described.

First Embodiment

FIG. 7 is a perspective view (partially ruptured view) illustrating aschematic configuration of a gas cell assembly according to a firstembodiment; FIG. 8 is a cross-sectional view taken along the line X-X inFIG. 7; and FIG. 9 is a development view of a shield case illustrated inFIG. 7. In FIGS. 7 and 8, descriptions will be made assuming that theleft side (an incidence side of the excitation light LL) of the drawingis a “front side”, the right side (an emission side of the excitationlight LL) thereof is a “rear side”, the top side thereof is an “upperside”, the bottom side thereof is a “lower side”, the front side thereofis a “right side”, and the depth side thereof is a “left side”.

As illustrated in FIG. 7, the gas cell assembly has a configuration inwhich the square columnar gas cell 31 is inserted into the squaretubular coil 35 which is wound, and the coil 35 into which the gas cell31 is inserted is stored in the shield case 9 containing a metalmaterial. Thus, the coil 35 is provided so as to surround an outercircumference of the gas cell 31 with the axis a (optical axis) of theexcitation light LL applied to the gas cell 31 as an axial direction.

The shield case 9 includes a box-shaped main body 90 and a lid 99 (righttabular portion) which covers an opening of the main body 90.

As illustrated in FIGS. 7 and 8, the main body 90 includes an uppertabular portion 91, a lower tabular portion 92, a front tabular portion93, a rear tabular portion 94, and a left tabular portion 95, and isformed by folding a single plate having the five tabular portions 91 to95 as illustrated in FIG. 9. The front tabular portion 93 and the reartabular portion 94 are respectively provided with through holes 931 and941 through which the excitation light LL passes.

In addition, pins 911 are formed at a front end and a rear end of a sidesurface of the upper tabular portion 91 on an opposite side to the lefttabular portion 95 so as to protrude outward, and pins 921 are formed ata front end and a rear end of a side surface of the lower tabularportion 92 on an opposite side to the left tabular portion 95 so as toprotrude outward. On the other hand, notches 991 are respectively formedat four corners of the lid (right tabular portion) 99.

In a state in which the lid 99 is installed at the main body 90 (anassembly state of the shield case 9), the four pins 911 and 921 arefitted to the corresponding notches 991 of the lid 99, and thus the lid99 is fixed to the main body 90. In addition, in this state, the mainbody 90 and the lid 99 may be joined to each other by using, forexample, adhesion using an adhesive, brazing, seam welding, and energyray welding (laser welding, electron ray welding, or the like).

In the invention, a main surface of one of two adjacent tabular portionsfaces a side surface of the other thereof, particularly, the twoadjacent tabular portions are located so that the side surface of theother tabular portion is included in a region of the main surface of onetabular portion when viewed from a direction perpendicular to the mainsurface of one tabular portion.

In the present embodiment, an inner surface (main surface) 912 of theupper tabular portion (one tabular portion) 91 faces an upper surface(side surface) 932 of the front tabular portion (the other tabularportion) 93 and an upper surface (side surface) 942 of the rear tabularportion (the other tabular portion) 94. In addition, an inner surface(main surface) 922 of the lower tabular portion (one tabular portion) 92faces a lower surface (side surface) 933 of the front tabular portion(the other tabular portion) 93 and a lower surface (side surface) 943 ofthe rear tabular portion (the other tabular portion) 94.

According to this configuration, since a magnetic field (a magneticline) generated by the coil 35 can pass through the shield case 9, themagnetic line of the magnetic field in the X axis direction can be madesubstantially parallel to the axis a of the excitation light LL. Thus,the magnetic field generated by the coil 35 can reliably act on thealkali metal atoms present in the inner space S.

With the configuration, thicknesses of the entire shield case 9 can bemade uniform, and thus a shield effect by the shield case 9 can besufficiently achieved.

As illustrated in FIG. 8, in an enlarged view of the corner of theshield case 9, a gap 901 is formed between, for example, the lowertabular portion 92 and the front tabular portion 93. However, since thegap 901 is present in the X axis direction of the shield case 9, even ifan external magnetic field enters the shield case 9 through the gap 901,the external magnetic field only travels substantially in parallel tothe inner surface 922 of the lower tabular portion 92 and thus does notdirectly travel toward the gas cell 31. For this reason, it is possibleto prevent the external magnetic field from unnecessarily acting on thealkali metal atoms present in the inner space S.

As mentioned above, in the invention, the shield case 9 having theabove-described configuration is used, and thus it is possible tostabilize a magnetic field of the inner space S of the gas cell 31 so asto further reduce a line width of the EIT signal, thereby realizing goodfrequency stability.

In contrast, as illustrated in FIG. 17, in a shield case 900 which isformed only by folding a sheet metal, a side surface of one of twoadjacent tabular portions does not surely face a side surface of theother thereof at a part (corner) where edges (tabular portions) of thesheet metal are close to or in contact with each other. For this reason,a magnetic field generated by the coil 35 does not smoothly pass throughthe shield case 900, and it is difficult for the magnetic line of themagnetic field in the X axis direction to be made substantially parallelto the axis a of the excitation light LL.

In this shield case 900, a sufficient thickness cannot be secured at thecorner. For this reason, a shield effect by the shield case 900 cannotbe sufficiently achieved. In an enlarged view of the corner, a gap 901is formed thereat, and, if an external magnetic field enters the shieldcase through the gap, the external magnetic field directly travelstoward the gas cell 31 and thus has an adverse effect on the alkalimetal atoms present in the inner space S of the gas cell 31.

As mentioned above, even if the shield case 900 of the related art isused, a magnetic field in the inner space S of the gas cell 31 cannot bestabilized, as a result, it is hard to reduce a line width of the EITsignal, and thus it is not possible to realize good frequency stability.

As described above, according to the invention, thicknesses of theentire shield case 9 are made uniform, that is, there is no part wherethe tabular portions 91 to 95 overlap each other in the shield case 9.This contributes to miniaturization of the shield case 9, and further,to miniaturization of the atomic oscillator 1.

The shield case 9 may contain a metal material; may be made of only ametal material; may be made of a resin material in which particles madeof a metal material are dispersed; and may be formed of a laminateincluding a metal layer made of a metal material and a resin layer madeof a resin material.

As the metal material, any metal material may be used as long as themetal material causes the shield case 9 to achieve a sufficient shieldeffect, but a soft magnetic material is preferably contained. As thesoft magnetic material, an alloy containing at least one of iron,nickel, chrome, and cobalt, and, particularly, permalloy is preferablyused. The soft magnetic material (particularly, permalloy) is used as ametal material, and thus it is possible to further improve a shieldeffect by the shield case 9.

An average thickness of the shield case 9 (the main body 90 (the tabularportions 91 to 95) and the lid (the right tabular portion) 99) is notparticularly limited, but is preferably about 0.05 mm to 1 mm, and ismore preferably about 0.1 mm to 0.7 mm. Consequently, it is possible toachieve a sufficient shield effect and miniaturization of the shieldcase 9.

Second Embodiment

Next, a gas cell assembly according to a second embodiment will bedescribed.

FIG. 10 is a cross-sectional view, corresponding to FIG. 8, of a gascell assembly according to the second embodiment.

Hereinafter, the second embodiment will be described focusing ondifferences from the first embodiment, and description of the samecontent will be omitted. In FIG. 10, the same constituent elements as inthe first embodiment are given the same reference numerals.

The second embodiment is the same as the first embodiment except that apositional relationship between the upper tabular portion 91 and thelower tabular portion 92, and between the front tabular portion 93 andthe rear tabular portion 94 are different.

In the second embodiment, the inner surface (main surface) 934 of thefront tabular portion (one tabular portion) 93 faces the front surface(side surface) 913 of the upper tabular portion (the other tabularportion) 91 and the front surface (side surface) 923 of the lowertabular portion (the other tabular portion) 92. In addition, the innersurface (main surface) 944 of the rear tabular portion (one tabularportion) 94 faces the rear surface (side surface) 914 of the uppertabular portion (the other tabular portion) 91 and the rear surface(side surface) 924 of the lower tabular portion (the other tabularportion) 92.

In other words, the front tabular portion 93 is disposed so that theinner surface 934 facing the front surfaces 913 and 923 of the uppertabular portion 91 and the lower tabular portion 92 intersects the axialdirection (the axis a of the excitation light LL) of the coil 35. Inaddition, the rear tabular portion 94 is disposed so that the innersurface 944 facing the rear surfaces 914 and 924 of the upper tabularportion 91 and the lower tabular portion 92 intersects the axialdirection of the coil 35.

It is possible to achieve the same operations and effects as in theshield case 9 of the first embodiment by using the shield case 9 of thesecond embodiment as well.

From the viewpoint of further reducing a line width of the EIT signal, amagnetic field (a loop of a magnetic line) is preferably furtherextended in the X axis direction than in the Y axis direction and the Zaxis direction. Here, the gap 901 is formed in the X axis direction atthe corner of the shield case 9 of the first embodiment. For thisreason, if a magnetic field is further extended in the X axis directionthan in the Y axis direction and the Z axis direction, most of magneticfields pass through the shield case 9, but, as illustrated in FIG. 8,there is a case where some of the magnetic fields may leak out of theshield case 9 through the gap 9, and thus disturbance may occur in themagnetic fields.

In contrast, in the shield case 9 of the second embodiment, since thegap 901 is formed in the Z axis direction, even if the magnetic fieldsare in the above-described state, the magnetic fields do not leak out ofthe shield case 9 through the gap 901, or, even if leakage occurs, aleakage amount thereof is extremely smaller than in the firstembodiment. Therefore, according to the shield case 9 of the secondembodiment, it is possible to stabilize a magnetic field in the innerspace S of the gas cell 31 more than in the shield case 9 of the firstembodiment, so as to further reduce a line width of the EIT signal,thereby realizing better frequency stability.

In relation to an external magnetic field, in the same manner as in thefirst embodiment, even if the external magnetic field enters the shieldcase 9 through the gap 901, the external magnetic field only travelssubstantially in parallel to the inner surface 934 of the lower tabularportion 93 and thus does not directly travel toward the gas cell 31. Forthis reason, it is possible to prevent the external magnetic field fromunnecessarily acting on the alkali metal atoms present in the innerspace S.

Third Embodiment

Next, a gas cell assembly according to a third embodiment will bedescribed.

FIG. 11 is a cross-sectional view, corresponding to FIG. 8, of a gascell assembly according to the third embodiment.

Hereinafter, the third embodiment will be described focusing ondifferences from the first and second embodiments, and description ofthe same content will be omitted. In FIG. 11, the same constituentelements as in the first and second embodiments are given the samereference numerals.

The third embodiment is the same as the second embodiment except thattwo adjacent tabular portions are joined to each other at a part where amain surface and a side surface face each other. Specifically, the uppertabular portion 91 and the lower tabular portion 92 are joined to thefront tabular portion 93 and the rear tabular portion 94 via a jointportion 902. In other words, the gap 901 is filled with the jointportion 902.

It is possible to achieve the same operations and effects as in theshield case 9 of the first and second embodiments by using the shieldcase 9 of the third embodiment as well.

The tabular portions 91 to 94 are joined to each other via the jointportion 902, and thus it is possible to improve a mechanical strength ofthe shield case 9. According to the configuration, it is possible toreliably prevent a size of the gap 901 from changing and also for thejoint portion 902 to prevent an external magnetic field from enteringthe shield case 9 through the gap 901. As a result, a magnetic field inthe inner space S of the gas cell 31 can be more reliably stabilized.

The joint portion 902 may be formed by using, for example, adhesionusing an adhesive, brazing, seam welding, and energy ray welding (laserwelding, electron ray welding, or the like). In addition, the jointportion 902 is preferably formed by using the same material as that ofthe shield case 9.

The tabular portions 91 to 94 of the first embodiment may be joined toeach other via the joint portion 902.

Fourth Embodiment

Next, a gas cell assembly according to a fourth embodiment will bedescribed.

FIG. 12 is a cross-sectional view, corresponding to FIG. 8, of a gascell assembly according to the fourth embodiment.

Hereinafter, the fourth embodiment will be described focusing ondifferences from the first and second embodiments, and description ofthe same content will be omitted. In FIG. 12, the same constituentelements as in the first and second embodiments are given the samereference numerals.

In the fourth embodiment, a positional relationship between the fronttabular portion 93, and the upper tabular portion 91 and the lowertabular portion 92 is the same as in the second embodiment, and apositional relationship between the rear tabular portion 94, and theupper tabular portion 91 and the lower tabular portion 92 is the same asin the first embodiment.

It is possible to achieve the same operations and effects as in theshield case 9 of the first to third embodiments by using the shield case9 of the fourth embodiment as well.

In the fourth embodiment, as illustrated in FIG. 12, the gas cell 31 ispreferably disposed to be shifted toward (biased toward) the fronttabular portion 93 side which allows a magnetic field to be easilystabilized. Consequently, it is possible to prevent or minimize aninstable state of a magnetic field in the inner space S of the gas cell31.

Fifth Embodiment

Next, a gas cell assembly according to a fifth embodiment will bedescribed.

FIG. 13 is a perspective view (partially ruptured view) illustrating aschematic configuration of a gas cell assembly according to the fifthembodiment, and FIG. 14 is a development view of a shield caseillustrated in FIG. 13. In FIG. 13, a description will be made assumingthat the left side (an incidence side of the excitation light LL) of thedrawing is a “front side”, the right side (an emission side of theexcitation light LL) thereof is a “rear side”, the top side thereof isan “upper side”, the bottom side thereof is a “lower side”, the frontside thereof is a “right side”, and the depth side thereof is a “leftside”.

Hereinafter, the fifth embodiment will be described focusing ondifferences from the first and second embodiments, and description ofthe same content will be omitted. In FIGS. 13 and 14, the sameconstituent elements as in the first and second embodiments are giventhe same reference numerals.

The fifth embodiment is the same as the first embodiment except for adifference in the entire shape of the gas cell assembly.

As illustrated in FIG. 13, the gas cell assembly has a configuration inwhich the columnar gas cell 31 is inserted into the cylindrical coil 35which is wound, and the coil 35 into which the gas cell 31 is insertedis stored in the shield case 9 containing a metal material. Thus, thecoil 35 is provided so as to surround an outer circumference of the gascell 31 with the axis a (optical axis) of the excitation light LLapplied to the gas cell 31 as an axial direction.

The shield case 9 includes a cylindrical body portion (tabular portion)96, a disc-shaped front tabular portion 93 which is provided to cover afront opening of the body portion 96, and a disc-shaped rear tabularportion 94 which is provided to cover a rear opening of the body portion96.

As illustrated in FIG. 14, the shield case 9 is formed by folding asingle plate having the three tabular portions 93, 94 and 96.

The body portion 96 is formed by bending a rectangular region of asingle plate in a cylindrical shape, and further by joining an uppersurface 961 to a lower surface 962. This joining may be performed byusing, for example, brazing, seam welding, and energy ray welding (laserwelding, electron ray welding, or the like). A joint member for joiningthe upper surface 961 and the lower 962 together may be interposedtherebetween.

In the present embodiment, an inner surface (main surface) 934 of thefront tabular portion (one tabular portion) 93 faces a front surface(side surface) 963 of the body portion (the other tabular portion) 96,and an inner surface (main surface) 944 of the rear tabular portion (onetabular portion) 94 faces a rear surface (side surface) 964 of the bodyportion (the other tabular portion) 96.

It is possible to achieve the same operations and effects as in theshield case 9 of the first to fourth embodiments by using the shieldcase 9 of the fifth embodiment as well.

The tabular portions 93, 94 and 96 may be joined to each other via thejoint portion 902 of the third embodiment.

In the above-described gas cell assembly, the gas cell 31 and the coil35 are provided in the shield case 9, but at least one of the lightdetection portion 32, the heater 33, and the temperature sensor 34 maybe provided therein, and all the constituent elements may be providedtherein. In a case where all of the gas cell 31, the light detectionportion 32, the heater 33, the temperature sensor 34, and the coil 35are provided, the second package 36 may be used as a shield case.

In the first to fourth embodiments, the main body 90 (the tabularportions 91 to 95) and the lid (right tabular portion) 99 may beintegrally formed together, that is, the shield case 9 may be formed byfolding a single plate having the main body 90 (the tabular portions 91to 95) and the lid (right tabular portion) 99.

2. Electronic Apparatus

The atomic oscillator as described above may be incorporated intovarious electronic apparatuses. These electronic apparatuses have highreliability.

Hereinafter, an electronic apparatus according to an embodiment of theinvention will be described.

FIG. 15 is a diagram illustrating a schematic system configuration in acase where the atomic oscillator according to the embodiments of theinvention is applied to a positioning system using a GPS satellite.

A positioning system 100 illustrated in FIG. 15 includes a GPS satellite200, a base station apparatus 300, and a GPS reception apparatus 400.

The GPS satellite 200 transmits positioning information (GPS signal).

The base station apparatus 300 includes, for example, a reception device302 which receives the positioning information from the GPS satellite200 via an antenna 301 which is installed at an electronic referencepoint (GPS Observation Network of Geographical Survey Institute), and atransmission device 304 which transmits the positioning informationreceived by the reception device 302 via an antenna 303.

Here, the reception device 302 is an electronic apparatus which includesthe atomic oscillator 1 according to the embodiment of the invention asa reference frequency oscillation source. The reception device 302 hashigh reliability. In addition, the positioning information received bythe reception device 302 is transmitted by the transmission device 304in real time.

The GPS reception apparatus 400 includes a satellite reception unit 402which receives the positioning information from the GPS satellite 200via an antenna 401, and a base station reception unit 404 which receivesthe positioning information from the base station apparatus 300 via anantenna 403.

3. Moving Object

FIG. 16 is a diagram illustrating an example of a moving objectaccording to an embodiment of the invention.

In FIG. 16, a moving object 1500 has a car body 1501 and four wheels1502, and the wheels 1502 are rotated by a power source (engine)provided in the car body 1501. The atomic oscillator 1 is built into themoving object 1500.

Such a moving object has high reliability.

In addition, electronic apparatuses having the atomic oscillator (thequantum interference device according to the embodiments of theinvention) according to the embodiment of the invention are not limitedthereto, and may be applied to, for example, a mobile phone, a digitalstill camera, an ink jet type ejection apparatus (for example, an inkjet printer), a personal computer (a mobile type personal computer or alaptop type personal computer), a television, a video camera, a videotape recorder, a car navigation apparatus, a pager, an electronicorganizer (including a communication function), an electronicdictionary, an electronic calculator, an electronic gaming machine, awordprocessor, a workstation, a videophone, a security televisionmonitor, an electronic binocular, a POS terminal, a medical apparatus(for example, an electronic thermometer, a sphygmomanometer, a bloodglucose monitoring system, an electrocardiographic apparatus, anultrasonic diagnostic apparatus, or an electronic endoscope), afish-finder, various measurement apparatuses, meters and gauges (forexample, meters and gauges of vehicles, aircrafts, and ships), a flightsimulator, a terrestrial digital broadcast, and a mobile phone basestation.

As mentioned above, the quantum interference device, the atomicoscillator, the electronic apparatus, and the moving object according tothe embodiments of the invention have been described with reference tothe drawings, but the invention is not limited thereto.

In the quantum interference device, the atomic oscillator, theelectronic apparatus, and the moving object according to the embodimentsof the invention, a configuration of each part according to theembodiments of the invention may be replaced with any configurationshowing the same function as in the above-described embodiments, and anyconfiguration may be added thereto.

The atomic oscillator according to the embodiments of the invention maycover a combination of arbitrary configurations of the respectiveembodiments.

For example, in the above-described embodiments, a structure in whichthe gas cell is disposed between the light emitting portion and thelight detection portion has been described as an example, but the lightemitting portion and the light detection portion may be disposed on thesame side as the gas cell, and light reflected at a surface of the gascell on an opposite side to the light emitting portion and the lightdetection portion or a mirror which is provided at the gas cell on anopposite side to the light emitting portion and the light detectionportion may be detected by the light detection portion.

In the above-described embodiments, a case where the first package, thesecond package, and the optical components are respectively engaged withthe through holes formed at the wiring board has been described as anexample, but the invention is not limited thereto. For example, thefirst package, the second package, and the optical components may bedisposed on one surface of the wiring board, and the first package, thesecond package, and the optical components may be held by a box-shapedor block-shaped holder, and the holder may be disposed on the wiringboard.

For example, the components stored in the first package and thecomponents and the optical components stored in the second package maybe stored in a single package. Consequently, it is possible to furtherminiaturize the atomic oscillator.

The quantum interference device according to the embodiments of theinvention may be applied to an atomic oscillator based on a method ofusing a double resonance phenomenon caused by light and microwaves.

What is claimed is:
 1. A quantum interference device comprising: a gascell into which metal atoms are sealed; a light emitting portion thatemits light including a pair of resonance light beams for resonating themetal atoms toward the metal atoms; a coil that is provided to surroundan outer circumference of the gas cell; and a shield case that storesthe gas cell and the coil and contains a metal material, wherein theshield case is constituted by a plurality of tabular portions, in theplurality of tabular portions, a first bottom length of each of firstand second sides of the bottom surface respectively connecting to thefirst and second side surfaces is shorter than a first side length ofeach side of the first and second side surfaces respectively connectingto the first and second sides of the bottom surface, in the plurality oftabular portions, a second bottom length of each of third and fourthsides of the bottom surface respectively connecting to the third andfourth side surfaces is longer than a second side length of each side ofthe third and fourth side surfaces respectively connecting to the thirdand fourth side of the bottom surface, and other two sides configuringthe second side length of each of the third and fourth side surfacesrespectively face edges of each main surface of the first and secondside surfaces.
 2. The quantum interference device according to claim 1,wherein the main surface intersects an axial direction of the coil. 3.The quantum interference device according to claim 1, wherein the metalmaterial includes a soft magnetic material.
 4. The quantum interferencedevice according to claim 3, wherein the soft magnetic material ispermalloy.
 5. An atomic oscillator comprising the quantum interferencedevice according to claim
 1. 6. An electronic apparatus comprising thequantum interference device according to claim
 1. 7. A moving objectcomprising the quantum interference device according to claim
 1. 8. Aquantum interference device comprising: a gas cell into which metalatoms are sealed; a light emitting portion that emits light including apair of resonance light beams for resonating the metal atoms toward themetal atoms; a coil that is provided to surround an outer circumferenceof the gas cell; and a shield case that stores the gas cell and thecoil, the shield case being made of a metal material, the shield casehaving top, bottom, and first through fourth side surfaces, wherein theshield case is constituted by a plurality of tabular portions, each ofthe plurality of tabular portions has front and back tabular mainsurfaces and first through fourth tabular side surfaces, and among theplurality of tabular portions, the front tabular main surface of one oftwo adjacent tabular portions directly faces an entire of one of thefirst through fourth tabular side surfaces of the other tabular portion.9. The quantum interference device according to claim 8, wherein thefront tabular main surface of the one of the two adjacent tabularportions intersects an axial direction of the coil.
 10. The quantuminterference device according to claim 8, wherein the metal materialincludes a soft magnetic material.
 11. The quantum interference deviceaccording to claim 10, wherein the soft magnetic material is permalloy.12. An atomic oscillator comprising the quantum interference deviceaccording to claim
 8. 13. An electronic apparatus comprising the quantuminterference device according to claim
 8. 14. A moving object comprisingthe quantum interference device according to claim
 8. 15. A quantuminterference device comprising: a gas cell into which metal atoms aresealed; a light emitting portion that emits light including a pair ofresonance light beams for resonating the metal atoms toward the metalatoms; a coil that is provided to surround an outer circumference of thegas cell; and a shield case that stores the gas cell and the coil, theshield case being made of a metal material, the shield case having top,bottom, and first through fourth side surfaces, wherein the shield caseis constituted by a plurality of tabular portions, each of the pluralityof tabular portions has front and back tabular main surfaces and firstthrough fourth tabular side surfaces, among the plurality of tabularportions, the front tabular main surface of one of two adjacent tabularportions directly faces an entire of one of the first through fourthtabular side surfaces of the other tabular portion, and the fronttabular main surface of the one of the two adjacent tabular portionsintersects an axial direction of the light.
 16. The quantum interferencedevice according to claim 15, wherein the front tabular main surface ofthe one of the two adjacent tabular portions intersects an axialdirection of the coil.
 17. The quantum interference device according toclaim 15, wherein the metal material includes a soft magnetic material.18. The quantum interference device according to claim 17, wherein thesoft magnetic material is permalloy.
 19. An atomic oscillator comprisingthe quantum interference device according to claim
 15. 20. An electronicapparatus comprising the quantum interference device according to claim15.
 21. A moving object comprising the quantum interference deviceaccording to claim 15.